This document is a reference manual for the LLVM assembly language.
LLVM is an SSA based representation that provides type safety,
low-level operations, flexibility, and the capability of representing
'all' high-level languages cleanly. It is the common code
representation used throughout all phases of the LLVM compilation
strategy.

The LLVM code representation is designed to be used in three
different forms: as an in-memory compiler IR, as an on-disk bitcode
representation (suitable for fast loading by a Just-In-Time compiler),
and as a human readable assembly language representation. This allows
LLVM to provide a powerful intermediate representation for efficient
compiler transformations and analysis, while providing a natural means
to debug and visualize the transformations. The three different forms
of LLVM are all equivalent. This document describes the human readable
representation and notation.

The LLVM representation aims to be light-weight and low-level
while being expressive, typed, and extensible at the same time. It
aims to be a "universal IR" of sorts, by being at a low enough level
that high-level ideas may be cleanly mapped to it (similar to how
microprocessors are "universal IR's", allowing many source languages to
be mapped to them). By providing type information, LLVM can be used as
the target of optimizations: for example, through pointer analysis, it
can be proven that a C automatic variable is never accessed outside of
the current function... allowing it to be promoted to a simple SSA
value instead of a memory location.

It is important to note that this document describes 'well formed'
LLVM assembly language. There is a difference between what the parser
accepts and what is considered 'well formed'. For example, the
following instruction is syntactically okay, but not well formed:

...because the definition of %x does not dominate all of
its uses. The LLVM infrastructure provides a verification pass that may
be used to verify that an LLVM module is well formed. This pass is
automatically run by the parser after parsing input assembly and by
the optimizer before it outputs bitcode. The violations pointed out
by the verifier pass indicate bugs in transformation passes or input to
the parser.

LLVM identifiers come in two basic types: global and local. Global
identifiers (functions, global variables) begin with the @ character. Local
identifiers (register names, types) begin with the % character. Additionally,
there are three different formats for identifiers, for different purposes:

Named values are represented as a string of characters with their prefix.
For example, %foo, @DivisionByZero, %a.really.long.identifier. The actual
regular expression used is '[%@][a-zA-Z$._][a-zA-Z$._0-9]*'.
Identifiers which require other characters in their names can be surrounded
with quotes. In this way, anything except a " character can
be used in a named value.

Unnamed values are represented as an unsigned numeric value with their
prefix. For example, %12, @2, %44.

LLVM requires that values start with a prefix for two reasons: Compilers
don't need to worry about name clashes with reserved words, and the set of
reserved words may be expanded in the future without penalty. Additionally,
unnamed identifiers allow a compiler to quickly come up with a temporary
variable without having to avoid symbol table conflicts.

Reserved words in LLVM are very similar to reserved words in other
languages. There are keywords for different opcodes
('add',
'bitcast',
'ret', etc...), for primitive type names ('void', 'i32', etc...),
and others. These reserved words cannot conflict with variable names, because
none of them start with a prefix character ('%' or '@').

Here is an example of LLVM code to multiply the integer variable
'%X' by 8:

This last way of multiplying %X by 8 illustrates several
important lexical features of LLVM:

Comments are delimited with a ';' and go until the end of
line.

Unnamed temporaries are created when the result of a computation is not
assigned to a named value.

Unnamed temporaries are numbered sequentially

...and it also shows a convention that we follow in this document. When
demonstrating instructions, we will follow an instruction with a comment that
defines the type and name of value produced. Comments are shown in italic
text.

LLVM programs are composed of "Module"s, each of which is a
translation unit of the input programs. Each module consists of
functions, global variables, and symbol table entries. Modules may be
combined together with the LLVM linker, which merges function (and
global variable) definitions, resolves forward declarations, and merges
symbol table entries. Here is an example of the "hello world" module:

In general, a module is made up of a list of global values,
where both functions and global variables are global values. Global values are
represented by a pointer to a memory location (in this case, a pointer to an
array of char, and a pointer to a function), and have one of the following linkage types.

Global values with internal linkage are only directly accessible by
objects in the current module. In particular, linking code into a module with
an internal global value may cause the internal to be renamed as necessary to
avoid collisions. Because the symbol is internal to the module, all
references can be updated. This corresponds to the notion of the
'static' keyword in C.

Globals with "linkonce" linkage are merged with other globals of
the same name when linkage occurs. This is typically used to implement
inline functions, templates, or other code which must be generated in each
translation unit that uses it. Unreferenced linkonce globals are
allowed to be discarded.

"weak" linkage is exactly the same as linkonce linkage,
except that unreferenced weak globals may not be discarded. This is
used for globals that may be emitted in multiple translation units, but that
are not guaranteed to be emitted into every translation unit that uses them.
One example of this are common globals in C, such as "int X;" at
global scope.

"appending" linkage may only be applied to global variables of
pointer to array type. When two global variables with appending linkage are
linked together, the two global arrays are appended together. This is the
LLVM, typesafe, equivalent of having the system linker append together
"sections" with identical names when .o files are linked.

"dllimport" linkage causes the compiler to reference a function
or variable via a global pointer to a pointer that is set up by the DLL
exporting the symbol. On Microsoft Windows targets, the pointer name is
formed by combining _imp__ and the function or variable name.

"dllexport" linkage causes the compiler to provide a global
pointer to a pointer in a DLL, so that it can be referenced with the
dllimport attribute. On Microsoft Windows targets, the pointer
name is formed by combining _imp__ and the function or variable
name.

For example, since the ".LC0"
variable is defined to be internal, if another module defined a ".LC0"
variable and was linked with this one, one of the two would be renamed,
preventing a collision. Since "main" and "puts" are
external (i.e., lacking any linkage declarations), they are accessible
outside of the current module.

It is illegal for a function declaration
to have any linkage type other than "externally visible", dllimport,
or extern_weak.

LLVM functions, calls
and invokes can all have an optional calling convention
specified for the call. The calling convention of any pair of dynamic
caller/callee must match, or the behavior of the program is undefined. The
following calling conventions are supported by LLVM, and more may be added in
the future:

"ccc" - The C calling convention:

This calling convention (the default if no other calling convention is
specified) matches the target C calling conventions. This calling convention
supports varargs function calls and tolerates some mismatch in the declared
prototype and implemented declaration of the function (as does normal C).

"fastcc" - The fast calling convention:

This calling convention attempts to make calls as fast as possible
(e.g. by passing things in registers). This calling convention allows the
target to use whatever tricks it wants to produce fast code for the target,
without having to conform to an externally specified ABI. Implementations of
this convention should allow arbitrary tail call optimization to be supported.
This calling convention does not support varargs and requires the prototype of
all callees to exactly match the prototype of the function definition.

"coldcc" - The cold calling convention:

This calling convention attempts to make code in the caller as efficient
as possible under the assumption that the call is not commonly executed. As
such, these calls often preserve all registers so that the call does not break
any live ranges in the caller side. This calling convention does not support
varargs and requires the prototype of all callees to exactly match the
prototype of the function definition.

"cc <n>" - Numbered convention:

Any calling convention may be specified by number, allowing
target-specific calling conventions to be used. Target specific calling
conventions start at 64.

More calling conventions can be added/defined on an as-needed basis, to
support pascal conventions or any other well-known target-independent
convention.

All Global Variables and Functions have one of the following visibility styles:

"default" - Default style:

On ELF, default visibility means that the declaration is visible to other
modules and, in shared libraries, means that the declared entity may be
overridden. On Darwin, default visibility means that the declaration is
visible to other modules. Default visibility corresponds to "external
linkage" in the language.

"hidden" - Hidden style:

Two declarations of an object with hidden visibility refer to the same
object if they are in the same shared object. Usually, hidden visibility
indicates that the symbol will not be placed into the dynamic symbol table,
so no other module (executable or shared library) can reference it
directly.

"protected" - Protected style:

On ELF, protected visibility indicates that the symbol will be placed in
the dynamic symbol table, but that references within the defining module will
bind to the local symbol. That is, the symbol cannot be overridden by another
module.

Global variables define regions of memory allocated at compilation time
instead of run-time. Global variables may optionally be initialized, may have
an explicit section to be placed in, and may have an optional explicit alignment
specified. A variable may be defined as "thread_local", which means that it
will not be shared by threads (each thread will have a separated copy of the
variable). A variable may be defined as a global "constant," which indicates
that the contents of the variable will never be modified (enabling better
optimization, allowing the global data to be placed in the read-only section of
an executable, etc). Note that variables that need runtime initialization
cannot be marked "constant" as there is a store to the variable.

LLVM explicitly allows declarations of global variables to be marked
constant, even if the final definition of the global is not. This capability
can be used to enable slightly better optimization of the program, but requires
the language definition to guarantee that optimizations based on the
'constantness' are valid for the translation units that do not include the
definition.

As SSA values, global variables define pointer values that are in
scope (i.e. they dominate) all basic blocks in the program. Global
variables always define a pointer to their "content" type because they
describe a region of memory, and all memory objects in LLVM are
accessed through pointers.

A global variable may be declared to reside in a target-specifc numbered
address space. For targets that support them, address spaces may affect how
optimizations are performed and/or what target instructions are used to access
the variable. The default address space is zero. The address space qualifier
must precede any other attributes.

LLVM allows an explicit section to be specified for globals. If the target
supports it, it will emit globals to the section specified.

An explicit alignment may be specified for a global. If not present, or if
the alignment is set to zero, the alignment of the global is set by the target
to whatever it feels convenient. If an explicit alignment is specified, the
global is forced to have at least that much alignment. All alignments must be
a power of 2.

For example, the following defines a global in a numbered address space with
an initializer, section, and alignment:

A function definition contains a list of basic blocks, forming the CFG for
the function. Each basic block may optionally start with a label (giving the
basic block a symbol table entry), contains a list of instructions, and ends
with a terminator instruction (such as a branch or
function return).

The first basic block in a function is special in two ways: it is immediately
executed on entrance to the function, and it is not allowed to have predecessor
basic blocks (i.e. there can not be any branches to the entry block of a
function). Because the block can have no predecessors, it also cannot have any
PHI nodes.

LLVM allows an explicit section to be specified for functions. If the target
supports it, it will emit functions to the section specified.

An explicit alignment may be specified for a function. If not present, or if
the alignment is set to zero, the alignment of the function is set by the target
to whatever it feels convenient. If an explicit alignment is specified, the
function is forced to have at least that much alignment. All alignments must be
a power of 2.

Aliases act as "second name" for the aliasee value (which can be either
function or global variable or bitcast of global value). Aliases may have an
optional linkage type, and an
optional visibility style.

Syntax:

The return type and each parameter of a function type may have a set of
parameter attributes associated with them. Parameter attributes are
used to communicate additional information about the result or parameters of
a function. Parameter attributes are considered to be part of the function,
not of the function type, so functions with different parameter attributes
can have the same function type.

Parameter attributes are simple keywords that follow the type specified. If
multiple parameter attributes are needed, they are space separated. For
example:

Note that any attributes for the function result (nounwind,
readonly) come immediately after the argument list.

Currently, only the following parameter attributes are defined:

zeroext

This indicates that the parameter should be zero extended just before
a call to this function.

signext

This indicates that the parameter should be sign extended just before
a call to this function.

inreg

This indicates that the parameter should be placed in register (if
possible) during assembling function call. Support for this attribute is
target-specific

byval

This indicates that the pointer parameter should really be passed by
value to the function. The attribute implies that a hidden copy of the
pointee is made between the caller and the callee, so the callee is unable
to modify the value in the callee. This attribute is only valid on llvm
pointer arguments. It is generally used to pass structs and arrays by
value, but is also valid on scalars (even though this is silly).

sret

This indicates that the parameter specifies the address of a structure
that is the return value of the function in the source program.

noalias

This indicates that the parameter not alias any other object or any
other "noalias" objects during the function call.

noreturn

This function attribute indicates that the function never returns. This
indicates to LLVM that every call to this function should be treated as if
an unreachable instruction immediately followed the call.

nounwind

This function attribute indicates that the function type does not use
the unwind instruction and does not allow stack unwinding to propagate
through it.

This function attribute indicates that the function has no side-effects
except for producing a return value or throwing an exception. The value
returned must only depend on the function arguments and/or global variables.
It may use values obtained by dereferencing pointers.

readnone

A readnone function has the same restrictions as a readonly
function, but in addition it is not allowed to dereference any pointer arguments
or global variables.

Modules may contain "module-level inline asm" blocks, which corresponds to the
GCC "file scope inline asm" blocks. These blocks are internally concatenated by
LLVM and treated as a single unit, but may be separated in the .ll file if
desired. The syntax is very simple:

module asm "inline asm code goes here"
module asm "more can go here"

The strings can contain any character by escaping non-printable characters.
The escape sequence used is simply "\xx" where "xx" is the two digit hex code
for the number.

The inline asm code is simply printed to the machine code .s file when
assembly code is generated.

A module may specify a target specific data layout string that specifies how
data is to be laid out in memory. The syntax for the data layout is simply:

target datalayout = "layout specification"

The layout specification consists of a list of specifications
separated by the minus sign character ('-'). Each specification starts with a
letter and may include other information after the letter to define some
aspect of the data layout. The specifications accepted are as follows:

E

Specifies that the target lays out data in big-endian form. That is, the
bits with the most significance have the lowest address location.

e

Specifies that hte target lays out data in little-endian form. That is,
the bits with the least significance have the lowest address location.

p:size:abi:pref

This specifies the size of a pointer and its abi and
preferred alignments. All sizes are in bits. Specifying the pref
alignment is optional. If omitted, the preceding : should be omitted
too.

isize:abi:pref

This specifies the alignment for an integer type of a given bit
size. The value of size must be in the range [1,2^23).

vsize:abi:pref

This specifies the alignment for a vector type of a given bit
size.

fsize:abi:pref

This specifies the alignment for a floating point type of a given bit
size. The value of size must be either 32 (float) or 64
(double).

asize:abi:pref

This specifies the alignment for an aggregate type of a given bit
size.

When constructing the data layout for a given target, LLVM starts with a
default set of specifications which are then (possibly) overriden by the
specifications in the datalayout keyword. The default specifications
are given in this list:

E - big endian

p:32:64:64 - 32-bit pointers with 64-bit alignment

i1:8:8 - i1 is 8-bit (byte) aligned

i8:8:8 - i8 is 8-bit (byte) aligned

i16:16:16 - i16 is 16-bit aligned

i32:32:32 - i32 is 32-bit aligned

i64:32:64 - i64 has abi alignment of 32-bits but preferred
alignment of 64-bits

f32:32:32 - float is 32-bit aligned

f64:64:64 - double is 64-bit aligned

v64:64:64 - 64-bit vector is 64-bit aligned

v128:128:128 - 128-bit vector is 128-bit aligned

a0:0:1 - aggregates are 8-bit aligned

When llvm is determining the alignment for a given type, it uses the
following rules:

If the type sought is an exact match for one of the specifications, that
specification is used.

If no match is found, and the type sought is an integer type, then the
smallest integer type that is larger than the bitwidth of the sought type is
used. If none of the specifications are larger than the bitwidth then the the
largest integer type is used. For example, given the default specifications
above, the i7 type will use the alignment of i8 (next largest) while both
i65 and i256 will use the alignment of i64 (largest specified).

If no match is found, and the type sought is a vector type, then the
largest vector type that is smaller than the sought vector type will be used
as a fall back. This happens because <128 x double> can be implemented in
terms of 64 <2 x double>, for example.

The LLVM type system is one of the most important features of the
intermediate representation. Being typed enables a number of
optimizations to be performed on the IR directly, without having to do
extra analyses on the side before the transformation. A strong type
system makes it easier to read the generated code and enables novel
analyses and transformations that are not feasible to perform on normal
three address code representations.

The first class types are perhaps the
most important. Values of these types are the only ones which can be
produced by instructions, passed as arguments, or used as operands to
instructions. This means that all structures and arrays must be
manipulated either by pointer or by component.

Overview:

Syntax:

Overview:

Syntax:

The real power in LLVM comes from the derived types in the system.
This is what allows a programmer to represent arrays, functions,
pointers, and other useful types. Note that these derived types may be
recursive: For example, it is possible to have a two dimensional array.

Syntax:

Examples:

Overview:

The array type is a very simple derived type that arranges elements
sequentially in memory. The array type requires a size (number of
elements) and an underlying data type.

Syntax:

[<# elements> x <elementtype>]

The number of elements is a constant integer value; elementtype may
be any type with a size.

Examples:

[40 x i32]

Array of 40 32-bit integer values.

[41 x i32]

Array of 41 32-bit integer values.

[4 x i8]

Array of 4 8-bit integer values.

Here are some examples of multidimensional arrays:

[3 x [4 x i32]]

3x4 array of 32-bit integer values.

[12 x [10 x float]]

12x10 array of single precision floating point values.

[2 x [3 x [4 x i16]]]

2x3x4 array of 16-bit integer values.

Note that 'variable sized arrays' can be implemented in LLVM with a zero
length array. Normally, accesses past the end of an array are undefined in
LLVM (e.g. it is illegal to access the 5th element of a 3 element array).
As a special case, however, zero length arrays are recognized to be variable
length. This allows implementation of 'pascal style arrays' with the LLVM
type "{ i32, [0 x float]}", for example.

Overview:

The function type can be thought of as a function signature. It
consists of a return type and a list of formal parameter types.
Function types are usually used to build virtual function tables
(which are structures of pointers to functions), for indirect function
calls, and when defining a function.

The return type of a function type cannot be an aggregate type.

Syntax:

<returntype> (<parameter list>)

...where '<parameter list>' is a comma-separated list of type
specifiers. Optionally, the parameter list may include a type ...,
which indicates that the function takes a variable number of arguments.
Variable argument functions can access their arguments with the variable argument handling intrinsic functions.

Examples:

i32 (i32)

function taking an i32, returning an i32

float (i16 signext, i32 *) *

Pointer to a function that takes
an i16 that should be sign extended and a
pointer to i32, returning
float.

i32 (i8*, ...)

A vararg function that takes at least one
pointer to i8 (char in C),
which returns an integer. This is the signature for printf in
LLVM.

Overview:

The structure type is used to represent a collection of data members
together in memory. The packing of the field types is defined to match
the ABI of the underlying processor. The elements of a structure may
be any type that has a size.

Structures are accessed using 'load
and 'store' by getting a pointer to a
field with the 'getelementptr'
instruction.

Syntax:

{ <type list> }

Examples:

{ i32, i32, i32 }

A triple of three i32 values

{ float, i32 (i32) * }

A pair, where the first element is a float and the
second element is a pointer to a
function that takes an i32, returning
an i32.

Overview:

The packed structure type is used to represent a collection of data members
together in memory. There is no padding between fields. Further, the alignment
of a packed structure is 1 byte. The elements of a packed structure may
be any type that has a size.

Structures are accessed using 'load
and 'store' by getting a pointer to a
field with the 'getelementptr'
instruction.

Syntax:

< { <type list> } >

Examples:

< { i32, i32, i32 } >

A triple of three i32 values

< { float, i32 (i32)* } >

A pair, where the first element is a float and the
second element is a pointer to a
function that takes an i32, returning
an i32.

Overview:

As in many languages, the pointer type represents a pointer or
reference to another object, which must live in memory. Pointer types may have
an optional address space attribute defining the target-specific numbered
address space where the pointed-to object resides. The default address space is
zero.

Overview:

A vector type is a simple derived type that represents a vector
of elements. Vector types are used when multiple primitive data
are operated in parallel using a single instruction (SIMD).
A vector type requires a size (number of
elements) and an underlying primitive data type. Vectors must have a power
of two length (1, 2, 4, 8, 16 ...). Vector types are
considered first class.

Syntax:

< <# elements> x <elementtype> >

The number of elements is a constant integer value; elementtype may
be any integer or floating point type.

Examples:

Overview:

Opaque types are used to represent unknown types in the system. This
corresponds (for example) to the C notion of a forward declared structure type.
In LLVM, opaque types can eventually be resolved to any type (not just a
structure type).

Syntax:

Examples:

The two strings 'true' and 'false' are both valid
constants of the i1 type.

Integer constants

Standard integers (such as '4') are constants of the integer type. Negative numbers may be used with
integer types.

Floating point constants

Floating point constants use standard decimal notation (e.g. 123.421),
exponential notation (e.g. 1.23421e+2), or a more precise hexadecimal
notation (see below). Floating point constants must have a floating point type.

Null pointer constants

The identifier 'null' is recognized as a null pointer constant
and must be of pointer type.

The one non-intuitive notation for constants is the optional hexadecimal form
of floating point constants. For example, the form 'double
0x432ff973cafa8000' is equivalent to (but harder to read than) 'double
4.5e+15'. The only time hexadecimal floating point constants are required
(and the only time that they are generated by the disassembler) is when a
floating point constant must be emitted but it cannot be represented as a
decimal floating point number. For example, NaN's, infinities, and other
special values are represented in their IEEE hexadecimal format so that
assembly and disassembly do not cause any bits to change in the constants.

Structure constants are represented with notation similar to structure
type definitions (a comma separated list of elements, surrounded by braces
({})). For example: "{ i32 4, float 17.0, i32* @G }",
where "@G" is declared as "@G = external global i32". Structure constants
must have structure type, and the number and
types of elements must match those specified by the type.

Array constants

Array constants are represented with notation similar to array type
definitions (a comma separated list of elements, surrounded by square brackets
([])). For example: "[ i32 42, i32 11, i32 74 ]". Array
constants must have array type, and the number and
types of elements must match those specified by the type.

Vector constants

Vector constants are represented with notation similar to vector type
definitions (a comma separated list of elements, surrounded by
less-than/greater-than's (<>)). For example: "< i32 42,
i32 11, i32 74, i32 100 >". Vector constants must have vector type, and the number and types of elements must
match those specified by the type.

Zero initialization

The string 'zeroinitializer' can be used to zero initialize a
value to zero of any type, including scalar and aggregate types.
This is often used to avoid having to print large zero initializers (e.g. for
large arrays) and is always exactly equivalent to using explicit zero
initializers.

Constant expressions are used to allow expressions involving other constants
to be used as constants. Constant expressions may be of any first class type and may involve any LLVM operation
that does not have side effects (e.g. load and call are not supported). The
following is the syntax for constant expressions:

trunc ( CST to TYPE )

Truncate a constant to another type. The bit size of CST must be larger
than the bit size of TYPE. Both types must be integers.

zext ( CST to TYPE )

Zero extend a constant to another type. The bit size of CST must be
smaller or equal to the bit size of TYPE. Both types must be integers.

sext ( CST to TYPE )

Sign extend a constant to another type. The bit size of CST must be
smaller or equal to the bit size of TYPE. Both types must be integers.

fptrunc ( CST to TYPE )

Truncate a floating point constant to another floating point type. The
size of CST must be larger than the size of TYPE. Both types must be
floating point.

fpext ( CST to TYPE )

Floating point extend a constant to another type. The size of CST must be
smaller or equal to the size of TYPE. Both types must be floating point.

fptoui ( CST to TYPE )

Convert a floating point constant to the corresponding unsigned integer
constant. TYPE must be a scalar or vector integer type. CST must be of scalar
or vector floating point type. Both CST and TYPE must be scalars, or vectors
of the same number of elements. If the value won't fit in the integer type,
the results are undefined.

fptosi ( CST to TYPE )

Convert a floating point constant to the corresponding signed integer
constant. TYPE must be a scalar or vector integer type. CST must be of scalar
or vector floating point type. Both CST and TYPE must be scalars, or vectors
of the same number of elements. If the value won't fit in the integer type,
the results are undefined.

uitofp ( CST to TYPE )

Convert an unsigned integer constant to the corresponding floating point
constant. TYPE must be a scalar or vector floating point type. CST must be of
scalar or vector integer type. Both CST and TYPE must be scalars, or vectors
of the same number of elements. If the value won't fit in the floating point
type, the results are undefined.

sitofp ( CST to TYPE )

Convert a signed integer constant to the corresponding floating point
constant. TYPE must be a scalar or vector floating point type. CST must be of
scalar or vector integer type. Both CST and TYPE must be scalars, or vectors
of the same number of elements. If the value won't fit in the floating point
type, the results are undefined.

ptrtoint ( CST to TYPE )

Convert a pointer typed constant to the corresponding integer constant
TYPE must be an integer type. CST must be of pointer type. The CST value is
zero extended, truncated, or unchanged to make it fit in TYPE.

inttoptr ( CST to TYPE )

Convert a integer constant to a pointer constant. TYPE must be a
pointer type. CST must be of integer type. The CST value is zero extended,
truncated, or unchanged to make it fit in a pointer size. This one is
really dangerous!

bitcast ( CST to TYPE )

Convert a constant, CST, to another TYPE. The size of CST and TYPE must be
identical (same number of bits). The conversion is done as if the CST value
was stored to memory and read back as TYPE. In other words, no bits change
with this operator, just the type. This can be used for conversion of
vector types to any other type, as long as they have the same bit width. For
pointers it is only valid to cast to another pointer type.

getelementptr ( CSTPTR, IDX0, IDX1, ... )

Perform the getelementptr operation on
constants. As with the getelementptr
instruction, the index list may have zero or more indexes, which are required
to make sense for the type of "CSTPTR".

Perform the specified operation of the LHS and RHS constants. OPCODE may
be any of the binary or bitwise
binary operations. The constraints on operands are the same as those for
the corresponding instruction (e.g. no bitwise operations on floating point
values are allowed).

LLVM supports inline assembler expressions (as opposed to
Module-Level Inline Assembly) through the use of a special value. This
value represents the inline assembler as a string (containing the instructions
to emit), a list of operand constraints (stored as a string), and a flag that
indicates whether or not the inline asm expression has side effects. An example
inline assembler expression is:

i32 (i32) asm "bswap $0", "=r,r"

Inline assembler expressions may only be used as the callee operand of
a call instruction. Thus, typically we have:

As mentioned previously, every
basic block in a program ends with a "Terminator" instruction, which
indicates which block should be executed after the current block is
finished. These terminator instructions typically yield a 'void'
value: they produce control flow, not values (the one exception being
the 'invoke' instruction).

There are six different terminator instructions: the 'ret' instruction, the 'br'
instruction, the 'switch' instruction,
the 'invoke' instruction, the 'unwind' instruction, and the 'unreachable' instruction.

Syntax:

Overview:

The 'ret' instruction is used to return control flow (and a
value) from a function back to the caller.

There are two forms of the 'ret' instruction: one that
returns a value and then causes control flow, and one that just causes
control flow to occur.

Arguments:

The 'ret' instruction may return any 'first class' type. Notice that a function is
not well formed if there exists a 'ret'
instruction inside of the function that returns a value that does not
match the return type of the function.

Semantics:

When the 'ret' instruction is executed, control flow
returns back to the calling function's context. If the caller is a "call" instruction, execution continues at
the instruction after the call. If the caller was an "invoke" instruction, execution continues
at the beginning of the "normal" destination block. If the instruction
returns a value, that value shall set the call or invoke instruction's
return value.

Example:

Syntax:

Overview:

The 'br' instruction is used to cause control flow to
transfer to a different basic block in the current function. There are
two forms of this instruction, corresponding to a conditional branch
and an unconditional branch.

Arguments:

The conditional branch form of the 'br' instruction takes a
single 'i1' value and two 'label' values. The
unconditional form of the 'br' instruction takes a single
'label' value as a target.

Semantics:

Upon execution of a conditional 'br' instruction, the 'i1'
argument is evaluated. If the value is true, control flows
to the 'iftrue' label argument. If "cond" is false,
control flows to the 'iffalse' label argument.

Syntax:

Overview:

The 'switch' instruction is used to transfer control flow to one of
several different places. It is a generalization of the 'br'
instruction, allowing a branch to occur to one of many possible
destinations.

Arguments:

The 'switch' instruction uses three parameters: an integer
comparison value 'value', a default 'label' destination, and
an array of pairs of comparison value constants and 'label's. The
table is not allowed to contain duplicate constant entries.

Semantics:

The switch instruction specifies a table of values and
destinations. When the 'switch' instruction is executed, this
table is searched for the given value. If the value is found, control flow is
transfered to the corresponding destination; otherwise, control flow is
transfered to the default destination.

Implementation:

Depending on properties of the target machine and the particular
switch instruction, this instruction may be code generated in different
ways. For example, it could be generated as a series of chained conditional
branches or with a lookup table.

Syntax:

Overview:

The 'invoke' instruction causes control to transfer to a specified
function, with the possibility of control flow transfer to either the
'normal' label or the
'exception' label. If the callee function returns with the
"ret" instruction, control flow will return to the
"normal" label. If the callee (or any indirect callees) returns with the "unwind" instruction, control is interrupted and
continued at the dynamically nearest "exception" label.

Arguments:

This instruction requires several arguments:

The optional "cconv" marker indicates which calling
convention the call should use. If none is specified, the call defaults
to using C calling conventions.

'ptr to function ty': shall be the signature of the pointer to
function value being invoked. In most cases, this is a direct function
invocation, but indirect invokes are just as possible, branching off
an arbitrary pointer to function value.

'function ptr val': An LLVM value containing a pointer to a
function to be invoked.

'function args': argument list whose types match the function
signature argument types. If the function signature indicates the function
accepts a variable number of arguments, the extra arguments can be
specified.

'normal label': the label reached when the called function
executes a 'ret' instruction.

'exception label': the label reached when a callee returns with
the unwind instruction.

Semantics:

This instruction is designed to operate as a standard 'call' instruction in most regards. The primary
difference is that it establishes an association with a label, which is used by
the runtime library to unwind the stack.

This instruction is used in languages with destructors to ensure that proper
cleanup is performed in the case of either a longjmp or a thrown
exception. Additionally, this is important for implementation of
'catch' clauses in high-level languages that support them.

Syntax:

unwind

Overview:

The 'unwind' instruction unwinds the stack, continuing control flow
at the first callee in the dynamic call stack which used an invoke instruction to perform the call. This is
primarily used to implement exception handling.

Semantics:

The 'unwind' intrinsic causes execution of the current function to
immediately halt. The dynamic call stack is then searched for the first invoke instruction on the call stack. Once found,
execution continues at the "exceptional" destination block specified by the
invoke instruction. If there is no invoke instruction in the
dynamic call chain, undefined behavior results.

Syntax:

unreachable

Overview:

The 'unreachable' instruction has no defined semantics. This
instruction is used to inform the optimizer that a particular portion of the
code is not reachable. This can be used to indicate that the code after a
no-return function cannot be reached, and other facts.

Semantics:

Binary operators are used to do most of the computation in a
program. They require two operands, execute an operation on them, and
produce a single value. The operands might represent
multiple data, as is the case with the vector data type.
The result value of a binary operator is not
necessarily the same type as its operands.

Example:

Syntax:

<result> = udiv <ty> <var1>, <var2> ; yields {ty}:result

Overview:

The 'udiv' instruction returns the quotient of its two
operands.

Arguments:

The two arguments to the 'udiv' instruction must be
integer values. Both arguments must have identical
types. This instruction can also take vector versions
of the values in which case the elements must be integers.

Semantics:

The value produced is the unsigned integer quotient of the two operands. This
instruction always performs an unsigned division operation, regardless of
whether the arguments are unsigned or not.

Example:

Syntax:

<result> = sdiv <ty> <var1>, <var2> ; yields {ty}:result

Overview:

The 'sdiv' instruction returns the quotient of its two
operands.

Arguments:

The two arguments to the 'sdiv' instruction must be
integer values. Both arguments must have identical
types. This instruction can also take vector versions
of the values in which case the elements must be integers.

Semantics:

The value produced is the signed integer quotient of the two operands. This
instruction always performs a signed division operation, regardless of whether
the arguments are signed or not.

Semantics:

Example:

Syntax:

<result> = urem <ty> <var1>, <var2> ; yields {ty}:result

Overview:

The 'urem' instruction returns the remainder from the
unsigned division of its two arguments.

Arguments:

The two arguments to the 'urem' instruction must be
integer values. Both arguments must have identical
types. This instruction can also take vector versions
of the values in which case the elements must be integers.

Semantics:

This instruction returns the unsigned integer remainder of a division.
This instruction always performs an unsigned division to get the remainder,
regardless of whether the arguments are unsigned or not.

Example:

Syntax:

Overview:

The 'srem' instruction returns the remainder from the
signed division of its two operands. This instruction can also take
vector versions of the values in which case
the elements must be integers.

Arguments:

The two arguments to the 'srem' instruction must be
integer values. Both arguments must have identical
types.

Semantics:

This instruction returns the remainder of a division (where the result
has the same sign as the dividend, var1), not the modulo
operator (where the result has the same sign as the divisor, var2) of
a value. For more information about the difference, see The
Math Forum. For a table of how this is implemented in various languages,
please see
Wikipedia: modulo operation.

Semantics:

Example:

Bitwise binary operators are used to do various forms of
bit-twiddling in a program. They are generally very efficient
instructions and can commonly be strength reduced from other
instructions. They require two operands, execute an operation on them,
and produce a single value. The resulting value of the bitwise binary
operators is always the same type as its first operand.

Syntax:

Overview:

The 'lshr' instruction (logical shift right) returns the first
operand shifted to the right a specified number of bits with zero fill.

Arguments:

Both arguments to the 'lshr' instruction must be the same
integer type.

Semantics:

This instruction always performs a logical shift right operation. The most
significant bits of the result will be filled with zero bits after the
shift. If var2 is (statically or dynamically) equal to or larger than
the number of bits in var1, the result is undefined.

Syntax:

Overview:

The 'ashr' instruction (arithmetic shift right) returns the first
operand shifted to the right a specified number of bits with sign extension.

Arguments:

Both arguments to the 'ashr' instruction must be the same
integer type.

Semantics:

This instruction always performs an arithmetic shift right operation,
The most significant bits of the result will be filled with the sign bit
of var1. If var2 is (statically or dynamically) equal to or
larger than the number of bits in var1, the result is undefined.

LLVM supports several instructions to represent vector operations in a
target-independent manner. These instructions cover the element-access and
vector-specific operations needed to process vectors effectively. While LLVM
does directly support these vector operations, many sophisticated algorithms
will want to use target-specific intrinsics to take full advantage of a specific
target.

Example:

Syntax:

Overview:

The 'insertelement' instruction inserts a scalar
element into a vector at a specified index.

Arguments:

The first operand of an 'insertelement' instruction is a
value of vector type. The second operand is a
scalar value whose type must equal the element type of the first
operand. The third operand is an index indicating the position at
which to insert the value. The index may be a variable.

Semantics:

The result is a vector of the same type as val. Its
element values are those of val except at position
idx, where it gets the value elt. If idx
exceeds the length of val, the results are undefined.

Example:

Syntax:

Overview:

The 'shufflevector' instruction constructs a permutation of elements
from two input vectors, returning a vector of the same type.

Arguments:

The first two operands of a 'shufflevector' instruction are vectors
with types that match each other and types that match the result of the
instruction. The third argument is a shuffle mask, which has the same number
of elements as the other vector type, but whose element type is always 'i32'.

The shuffle mask operand is required to be a constant vector with either
constant integer or undef values.

Semantics:

The elements of the two input vectors are numbered from left to right across
both of the vectors. The shuffle mask operand specifies, for each element of
the result vector, which element of the two input registers the result element
gets. The element selector may be undef (meaning "don't care") and the second
operand may be undef if performing a shuffle from only one vector.

A key design point of an SSA-based representation is how it
represents memory. In LLVM, no memory locations are in SSA form, which
makes things very simple. This section describes how to read, write,
allocate, and free memory in LLVM.

Syntax:

Overview:

The 'malloc' instruction allocates memory from the system
heap and returns a pointer to it. The object is always allocated in the generic
address space (address space zero).

Arguments:

The 'malloc' instruction allocates
sizeof(<type>)*NumElements
bytes of memory from the operating system and returns a pointer of the
appropriate type to the program. If "NumElements" is specified, it is the
number of elements allocated. If an alignment is specified, the value result
of the allocation is guaranteed to be aligned to at least that boundary. If
not specified, or if zero, the target can choose to align the allocation on any
convenient boundary.

'type' must be a sized type.

Semantics:

Memory is allocated using the system "malloc" function, and
a pointer is returned.

Example:

Syntax:

Overview:

The 'alloca' instruction allocates memory on the stack frame of the
currently executing function, to be automatically released when this function
returns to its caller. The object is always allocated in the generic address
space (address space zero).

Arguments:

The 'alloca' instruction allocates sizeof(<type>)*NumElements
bytes of memory on the runtime stack, returning a pointer of the
appropriate type to the program. If "NumElements" is specified, it is the
number of elements allocated. If an alignment is specified, the value result
of the allocation is guaranteed to be aligned to at least that boundary. If
not specified, or if zero, the target can choose to align the allocation on any
convenient boundary.

'type' may be any sized type.

Semantics:

Memory is allocated; a pointer is returned. 'alloca'd
memory is automatically released when the function returns. The 'alloca'
instruction is commonly used to represent automatic variables that must
have an address available. When the function returns (either with the ret or unwind
instructions), the memory is reclaimed.

Syntax:

Overview:

The 'load' instruction is used to read from memory.

Arguments:

The argument to the 'load' instruction specifies the memory
address from which to load. The pointer must point to a first class type. If the load is
marked as volatile, then the optimizer is not allowed to modify
the number or order of execution of this load with other
volatile load and store
instructions.

The optional "align" argument specifies the alignment of the operation
(that is, the alignment of the memory address). A value of 0 or an
omitted "align" argument means that the operation has the preferential
alignment for the target. It is the responsibility of the code emitter
to ensure that the alignment information is correct. Overestimating
the alignment results in an undefined behavior. Underestimating the
alignment may produce less efficient code. An alignment of 1 is always
safe.

Syntax:

Overview:

The 'store' instruction is used to write to memory.

Arguments:

There are two arguments to the 'store' instruction: a value
to store and an address at which to store it. The type of the '<pointer>'
operand must be a pointer to the type of the '<value>'
operand. If the store is marked as volatile, then the
optimizer is not allowed to modify the number or order of execution of
this store with other volatile load and store instructions.

The optional "align" argument specifies the alignment of the operation
(that is, the alignment of the memory address). A value of 0 or an
omitted "align" argument means that the operation has the preferential
alignment for the target. It is the responsibility of the code emitter
to ensure that the alignment information is correct. Overestimating
the alignment results in an undefined behavior. Underestimating the
alignment may produce less efficient code. An alignment of 1 is always
safe.

Semantics:

The contents of memory are updated to contain '<value>'
at the location specified by the '<pointer>' operand.

Example:

Syntax:

<result> = getelementptr <ty>* <ptrval>{, <ty> <idx>}*

Overview:

The 'getelementptr' instruction is used to get the address of a
subelement of an aggregate data structure.

Arguments:

This instruction takes a list of integer operands that indicate what
elements of the aggregate object to index to. The actual types of the arguments
provided depend on the type of the first pointer argument. The
'getelementptr' instruction is used to index down through the type
levels of a structure or to a specific index in an array. When indexing into a
structure, only i32 integer constants are allowed. When indexing
into an array or pointer, only integers of 32 or 64 bits are allowed, and will
be sign extended to 64-bit values.

For example, let's consider a C code fragment and how it gets
compiled to LLVM:

Semantics:

The index types specified for the 'getelementptr' instruction depend
on the pointer type that is being indexed into. Pointer
and array types can use a 32-bit or 64-bit
integer type but the value will always be sign extended
to 64-bits. Structure types require i32constants.

In the example above, the first index is indexing into the '%ST*'
type, which is a pointer, yielding a '%ST' = '{ i32, double, %RT
}' type, a structure. The second index indexes into the third element of
the structure, yielding a '%RT' = '{ i8 , [10 x [20 x i32]],
i8 }' type, another structure. The third index indexes into the second
element of the structure, yielding a '[10 x [20 x i32]]' type, an
array. The two dimensions of the array are subscripted into, yielding an
'i32' type. The 'getelementptr' instruction returns a pointer
to this element, thus computing a value of 'i32*' type.

Note that it is perfectly legal to index partially through a
structure, returning a pointer to an inner element. Because of this,
the LLVM code for the given testcase is equivalent to:

Note that it is undefined to access an array out of bounds: array and
pointer indexes must always be within the defined bounds of the array type.
The one exception for this rules is zero length arrays. These arrays are
defined to be accessible as variable length arrays, which requires access
beyond the zero'th element.

The getelementptr instruction is often confusing. For some more insight
into how it works, see the getelementptr
FAQ.

Syntax:

<result> = trunc <ty> <value> to <ty2> ; yields ty2

Overview:

The 'trunc' instruction truncates its operand to the type ty2.

Arguments:

The 'trunc' instruction takes a value to trunc, which must
be an integer type, and a type that specifies the size
and type of the result, which must be an integer
type. The bit size of value must be larger than the bit size of
ty2. Equal sized types are not allowed.

Semantics:

The 'trunc' instruction truncates the high order bits in value
and converts the remaining bits to ty2. Since the source size must be
larger than the destination size, trunc cannot be a no-op cast.
It will always truncate bits.

Example:

Syntax:

<result> = zext <ty> <value> to <ty2> ; yields ty2

Overview:

The 'zext' instruction zero extends its operand to type
ty2.

Arguments:

The 'zext' instruction takes a value to cast, which must be of
integer type, and a type to cast it to, which must
also be of integer type. The bit size of the
value must be smaller than the bit size of the destination type,
ty2.

Semantics:

The zext fills the high order bits of the value with zero
bits until it reaches the size of the destination type, ty2.

Example:

Syntax:

<result> = sext <ty> <value> to <ty2> ; yields ty2

Overview:

The 'sext' sign extends value to the type ty2.

Arguments:

The 'sext' instruction takes a value to cast, which must be of
integer type, and a type to cast it to, which must
also be of integer type. The bit size of the
value must be smaller than the bit size of the destination type,
ty2.

Semantics:

The 'sext' instruction performs a sign extension by copying the sign
bit (highest order bit) of the value until it reaches the bit size of
the type ty2.

Example:

Syntax:

<result> = fptrunc <ty> <value> to <ty2> ; yields ty2

Overview:

The 'fptrunc' instruction truncates value to type
ty2.

Arguments:

The 'fptrunc' instruction takes a floating
point value to cast and a floating point type to
cast it to. The size of value must be larger than the size of
ty2. This implies that fptrunc cannot be used to make a
no-op cast.

Semantics:

The 'fptrunc' instruction truncates a value from a larger
floating point type to a smaller
floating point type. If the value cannot fit within
the destination type, ty2, then the results are undefined.

Syntax:

Overview:

The 'fpext' extends a floating point value to a larger
floating point value.

Arguments:

The 'fpext' instruction takes a
floating pointvalue to cast,
and a floating point type to cast it to. The source
type must be smaller than the destination type.

Semantics:

The 'fpext' instruction extends the value from a smaller
floating point type to a larger
floating point type. The fpext cannot be
used to make a no-op cast because it always changes bits. Use
bitcast to make a no-op cast for a floating point cast.

Example:

Syntax:

<result> = fptoui <ty> <value> to <ty2> ; yields ty2

Overview:

The 'fptoui' converts a floating point value to its
unsigned integer equivalent of type ty2.

Arguments:

The 'fptoui' instruction takes a value to cast, which must be a
scalar or vector floating point value, and a type
to cast it to ty2, which must be an integer
type. If ty is a vector floating point type, ty2 must be a
vector integer type with the same number of elements as ty

Semantics:

The 'fptoui' instruction converts its
floating point operand into the nearest (rounding
towards zero) unsigned integer value. If the value cannot fit in ty2,
the results are undefined.

Syntax:

Overview:

Arguments:

The 'fptosi' instruction takes a value to cast, which must be a
scalar or vector floating point value, and a type
to cast it to ty2, which must be an integer
type. If ty is a vector floating point type, ty2 must be a
vector integer type with the same number of elements as ty

Semantics:

The 'fptosi' instruction converts its
floating point operand into the nearest (rounding
towards zero) signed integer value. If the value cannot fit in ty2,
the results are undefined.

Example:

Syntax:

<result> = uitofp <ty> <value> to <ty2> ; yields ty2

Overview:

The 'uitofp' instruction regards value as an unsigned
integer and converts that value to the ty2 type.

Arguments:

The 'uitofp' instruction takes a value to cast, which must be a
scalar or vector integer value, and a type to cast it
to ty2, which must be an floating point
type. If ty is a vector integer type, ty2 must be a vector
floating point type with the same number of elements as ty

Semantics:

The 'uitofp' instruction interprets its operand as an unsigned
integer quantity and converts it to the corresponding floating point value. If
the value cannot fit in the floating point value, the results are undefined.

Example:

Syntax:

<result> = sitofp <ty> <value> to <ty2> ; yields ty2

Overview:

The 'sitofp' instruction regards value as a signed
integer and converts that value to the ty2 type.

Arguments:

The 'sitofp' instruction takes a value to cast, which must be a
scalar or vector integer value, and a type to cast it
to ty2, which must be an floating point
type. If ty is a vector integer type, ty2 must be a vector
floating point type with the same number of elements as ty

Semantics:

The 'sitofp' instruction interprets its operand as a signed
integer quantity and converts it to the corresponding floating point value. If
the value cannot fit in the floating point value, the results are undefined.

Example:

Syntax:

Overview:

The 'ptrtoint' instruction converts the pointer value to
the integer type ty2.

Arguments:

The 'ptrtoint' instruction takes a value to cast, which
must be a pointer value, and a type to cast it to
ty2, which must be an integer type.

Semantics:

The 'ptrtoint' instruction converts value to integer type
ty2 by interpreting the pointer value as an integer and either
truncating or zero extending that value to the size of the integer type. If
value is smaller than ty2 then a zero extension is done. If
value is larger than ty2 then a truncation is done. If they
are the same size, then nothing is done (no-op cast) other than a type
change.

Syntax:

Overview:

The 'inttoptr' instruction converts an integer value to
a pointer type, ty2.

Arguments:

The 'inttoptr' instruction takes an integer
value to cast, and a type to cast it to, which must be a
pointer type.

Semantics:

The 'inttoptr' instruction converts value to type
ty2 by applying either a zero extension or a truncation depending on
the size of the integer value. If value is larger than the
size of a pointer then a truncation is done. If value is smaller than
the size of a pointer then a zero extension is done. If they are the same size,
nothing is done (no-op cast).

Syntax:

<result> = bitcast <ty> <value> to <ty2> ; yields ty2

Overview:

The 'bitcast' instruction converts value to type
ty2 without changing any bits.

Arguments:

The 'bitcast' instruction takes a value to cast, which must be
a first class value, and a type to cast it to, which must also be a first class type. The bit sizes of value
and the destination type, ty2, must be identical. If the source
type is a pointer, the destination type must also be a pointer.

Semantics:

The 'bitcast' instruction converts value to type
ty2. It is always a no-op cast because no bits change with
this conversion. The conversion is done as if the value had been
stored to memory and read back as type ty2. Pointer types may only be
converted to other pointer types with this instruction. To convert pointers to
other types, use the inttoptr or
ptrtoint instructions first.

Syntax:

<result> = phi <ty> [ <val0>, <label0>], ...

Overview:

The 'phi' instruction is used to implement the φ node in
the SSA graph representing the function.

Arguments:

The type of the incoming values is specified with the first type
field. After this, the 'phi' instruction takes a list of pairs
as arguments, with one pair for each predecessor basic block of the
current block. Only values of first class
type may be used as the value arguments to the PHI node. Only labels
may be used as the label arguments.

There must be no non-phi instructions between the start of a basic
block and the PHI instructions: i.e. PHI instructions must be first in
a basic block.

Semantics:

At runtime, the 'phi' instruction logically takes on the value
specified by the pair corresponding to the predecessor basic block that executed
just prior to the current block.

Example:

Syntax:

Overview:

The 'call' instruction represents a simple function call.

Arguments:

This instruction requires several arguments:

The optional "tail" marker indicates whether the callee function accesses
any allocas or varargs in the caller. If the "tail" marker is present, the
function call is eligible for tail call optimization. Note that calls may
be marked "tail" even if they do not occur before a ret instruction.

The optional "cconv" marker indicates which calling
convention the call should use. If none is specified, the call defaults
to using C calling conventions.

'ty': the type of the call instruction itself which is also
the type of the return value. Functions that return no value are marked
void.

'fnty': shall be the signature of the pointer to function
value being invoked. The argument types must match the types implied by
this signature. This type can be omitted if the function is not varargs
and if the function type does not return a pointer to a function.

'fnptrval': An LLVM value containing a pointer to a function to
be invoked. In most cases, this is a direct function invocation, but
indirect calls are just as possible, calling an arbitrary pointer
to function value.

'function args': argument list whose types match the
function signature argument types. All arguments must be of
first class type. If the function signature
indicates the function accepts a variable number of arguments, the extra
arguments can be specified.

Semantics:

The 'call' instruction is used to cause control flow to
transfer to a specified function, with its incoming arguments bound to
the specified values. Upon a 'ret'
instruction in the called function, control flow continues with the
instruction after the function call, and the return value of the
function is bound to the result argument. This is a simpler case of
the invoke instruction.

Syntax:

Overview:

The 'va_arg' instruction is used to access arguments passed through
the "variable argument" area of a function call. It is used to implement the
va_arg macro in C.

Arguments:

This instruction takes a va_list* value and the type of
the argument. It returns a value of the specified argument type and
increments the va_list to point to the next argument. The
actual type of va_list is target specific.

Semantics:

The 'va_arg' instruction loads an argument of the specified
type from the specified va_list and causes the
va_list to point to the next argument. For more information,
see the variable argument handling Intrinsic
Functions.

It is legal for this instruction to be called in a function which does not
take a variable number of arguments, for example, the vfprintf
function.

va_arg is an LLVM instruction instead of an intrinsic function because it takes a type as an
argument.

Example:

LLVM supports the notion of an "intrinsic function". These functions have
well known names and semantics and are required to follow certain restrictions.
Overall, these intrinsics represent an extension mechanism for the LLVM
language that does not require changing all of the transformations in LLVM when
adding to the language (or the bitcode reader/writer, the parser, etc...).

Intrinsic function names must all start with an "llvm." prefix. This
prefix is reserved in LLVM for intrinsic names; thus, function names may not
begin with this prefix. Intrinsic functions must always be external functions:
you cannot define the body of intrinsic functions. Intrinsic functions may
only be used in call or invoke instructions: it is illegal to take the address
of an intrinsic function. Additionally, because intrinsic functions are part
of the LLVM language, it is required if any are added that they be documented
here.

Some intrinsic functions can be overloaded, i.e., the intrinsic represents
a family of functions that perform the same operation but on different data
types. Because LLVM can represent over 8 million different integer types,
overloading is used commonly to allow an intrinsic function to operate on any
integer type. One or more of the argument types or the result type can be
overloaded to accept any integer type. Argument types may also be defined as
exactly matching a previous argument's type or the result type. This allows an
intrinsic function which accepts multiple arguments, but needs all of them to
be of the same type, to only be overloaded with respect to a single argument or
the result.

Overloaded intrinsics will have the names of its overloaded argument types
encoded into its function name, each preceded by a period. Only those types
which are overloaded result in a name suffix. Arguments whose type is matched
against another type do not. For example, the llvm.ctpop function can
take an integer of any width and returns an integer of exactly the same integer
width. This leads to a family of functions such as
i8 @llvm.ctpop.i8(i8 %val) and i29 @llvm.ctpop.i29(i29 %val).
Only one type, the return type, is overloaded, and only one type suffix is
required. Because the argument's type is matched against the return type, it
does not require its own name suffix.

Variable argument support is defined in LLVM with the va_arg instruction and these three
intrinsic functions. These functions are related to the similarly
named macros defined in the <stdarg.h> header file.

All of these functions operate on arguments that use a
target-specific value type "va_list". The LLVM assembly
language reference manual does not define what this type is, so all
transformations should be prepared to handle these functions regardless of
the type used.

This example shows how the va_arg
instruction and the variable argument handling intrinsic functions are
used.

Syntax:

Overview:

The 'llvm.va_start' intrinsic initializes
*<arglist> for subsequent use by va_arg.

Arguments:

The argument is a pointer to a va_list element to initialize.

Semantics:

The 'llvm.va_start' intrinsic works just like the va_start
macro available in C. In a target-dependent way, it initializes the
va_list element to which the argument points, so that the next call to
va_arg will produce the first variable argument passed to the function.
Unlike the C va_start macro, this intrinsic does not need to know the
last argument of the function as the compiler can figure that out.

Syntax:

Overview:

Arguments:

The argument is a pointer to a va_list to destroy.

Semantics:

The 'llvm.va_end' intrinsic works just like the va_end
macro available in C. In a target-dependent way, it destroys the
va_list element to which the argument points. Calls to llvm.va_start and llvm.va_copy must be matched exactly with calls to
llvm.va_end.

Syntax:

Overview:

The 'llvm.va_copy' intrinsic copies the current argument position
from the source argument list to the destination argument list.

Arguments:

The first argument is a pointer to a va_list element to initialize.
The second argument is a pointer to a va_list element to copy from.

Semantics:

The 'llvm.va_copy' intrinsic works just like the va_copy
macro available in C. In a target-dependent way, it copies the source
va_list element into the destination va_list element. This
intrinsic is necessary because the
llvm.va_start intrinsic may be arbitrarily complex and require, for
example, memory allocation.

Syntax:

Overview:

The 'llvm.gcroot' intrinsic declares the existence of a GC root to
the code generator, and allows some metadata to be associated with it.

Arguments:

The first argument specifies the address of a stack object that contains the
root pointer. The second pointer (which must be either a constant or a global
value address) contains the meta-data to be associated with the root.

Semantics:

At runtime, a call to this intrinsics stores a null pointer into the "ptrloc"
location. At compile-time, the code generator generates information to allow
the runtime to find the pointer at GC safe points. The 'llvm.gcroot'
intrinsic may only be used in a function which specifies a GC
algorithm.

Overview:

Arguments:

The second argument is the address to read from, which should be an address
allocated from the garbage collector. The first object is a pointer to the
start of the referenced object, if needed by the language runtime (otherwise
null).

Semantics:

The 'llvm.gcread' intrinsic has the same semantics as a load
instruction, but may be replaced with substantially more complex code by the
garbage collector runtime, as needed. The 'llvm.gcread' intrinsic
may only be used in a function which specifies a GC
algorithm.

Arguments:

The first argument is the reference to store, the second is the start of the
object to store it to, and the third is the address of the field of Obj to
store to. If the runtime does not require a pointer to the object, Obj may be
null.

Semantics:

The 'llvm.gcwrite' intrinsic has the same semantics as a store
instruction, but may be replaced with substantially more complex code by the
garbage collector runtime, as needed. The 'llvm.gcwrite' intrinsic
may only be used in a function which specifies a GC
algorithm.

Syntax:

Overview:

The 'llvm.returnaddress' intrinsic attempts to compute a
target-specific value indicating the return address of the current function
or one of its callers.

Arguments:

The argument to this intrinsic indicates which function to return the address
for. Zero indicates the calling function, one indicates its caller, etc. The
argument is required to be a constant integer value.

Semantics:

The 'llvm.returnaddress' intrinsic either returns a pointer indicating
the return address of the specified call frame, or zero if it cannot be
identified. The value returned by this intrinsic is likely to be incorrect or 0
for arguments other than zero, so it should only be used for debugging purposes.

Note that calling this intrinsic does not prevent function inlining or other
aggressive transformations, so the value returned may not be that of the obvious
source-language caller.

Syntax:

declare i8 *@llvm.frameaddress(i32 <level>)

Overview:

The 'llvm.frameaddress' intrinsic attempts to return the
target-specific frame pointer value for the specified stack frame.

Arguments:

The argument to this intrinsic indicates which function to return the frame
pointer for. Zero indicates the calling function, one indicates its caller,
etc. The argument is required to be a constant integer value.

Semantics:

The 'llvm.frameaddress' intrinsic either returns a pointer indicating
the frame address of the specified call frame, or zero if it cannot be
identified. The value returned by this intrinsic is likely to be incorrect or 0
for arguments other than zero, so it should only be used for debugging purposes.

Note that calling this intrinsic does not prevent function inlining or other
aggressive transformations, so the value returned may not be that of the obvious
source-language caller.

Syntax:

declare i8 *@llvm.stacksave()

Overview:

The 'llvm.stacksave' intrinsic is used to remember the current state of
the function stack, for use with llvm.stackrestore. This is useful for implementing language
features like scoped automatic variable sized arrays in C99.

Semantics:

This intrinsic returns a opaque pointer value that can be passed to llvm.stackrestore. When an
llvm.stackrestore intrinsic is executed with a value saved from
llvm.stacksave, it effectively restores the state of the stack to the
state it was in when the llvm.stacksave intrinsic executed. In
practice, this pops any alloca blocks from the stack
that were allocated after the llvm.stacksave was executed.

Syntax:

declare void @llvm.stackrestore(i8 * %ptr)

Overview:

The 'llvm.stackrestore' intrinsic is used to restore the state of
the function stack to the state it was in when the corresponding llvm.stacksave intrinsic executed. This is
useful for implementing language features like scoped automatic variable sized
arrays in C99.

Semantics:

Syntax:

declare void @llvm.prefetch(i8* <address>, i32 <rw>, i32 <locality>)

Overview:

The 'llvm.prefetch' intrinsic is a hint to the code generator to insert
a prefetch instruction if supported; otherwise, it is a noop. Prefetches have
no
effect on the behavior of the program but can change its performance
characteristics.

Arguments:

address is the address to be prefetched, rw is the specifier
determining if the fetch should be for a read (0) or write (1), and
locality is a temporal locality specifier ranging from (0) - no
locality, to (3) - extremely local keep in cache. The rw and
locality arguments must be constant integers.

Semantics:

This intrinsic does not modify the behavior of the program. In particular,
prefetches cannot trap and do not produce a value. On targets that support this
intrinsic, the prefetch can provide hints to the processor cache for better
performance.

Syntax:

declare void @llvm.pcmarker(i32 <id>)

Overview:

The 'llvm.pcmarker' intrinsic is a method to export a Program Counter
(PC) in a region of
code to simulators and other tools. The method is target specific, but it is
expected that the marker will use exported symbols to transmit the PC of the marker.
The marker makes no guarantees that it will remain with any specific instruction
after optimizations. It is possible that the presence of a marker will inhibit
optimizations. The intended use is to be inserted after optimizations to allow
correlations of simulation runs.

Arguments:

id is a numerical id identifying the marker.

Semantics:

This intrinsic does not modify the behavior of the program. Backends that do not
support this intrinisic may ignore it.

Syntax:

declare i64 @llvm.readcyclecounter( )

Overview:

The 'llvm.readcyclecounter' intrinsic provides access to the cycle
counter register (or similar low latency, high accuracy clocks) on those targets
that support it. On X86, it should map to RDTSC. On Alpha, it should map to RPCC.
As the backing counters overflow quickly (on the order of 9 seconds on alpha), this
should only be used for small timings.

Semantics:

When directly supported, reading the cycle counter should not modify any memory.
Implementations are allowed to either return a application specific value or a
system wide value. On backends without support, this is lowered to a constant 0.

LLVM provides intrinsics for a few important standard C library functions.
These intrinsics allow source-language front-ends to pass information about the
alignment of the pointer arguments to the code generator, providing opportunity
for more efficient code generation.

Syntax:

Overview:

The 'llvm.memcpy.*' intrinsics copy a block of memory from the source
location to the destination location.

Note that, unlike the standard libc function, the llvm.memcpy.*
intrinsics do not return a value, and takes an extra alignment argument.

Arguments:

The first argument is a pointer to the destination, the second is a pointer to
the source. The third argument is an integer argument
specifying the number of bytes to copy, and the fourth argument is the alignment
of the source and destination locations.

If the call to this intrinisic has an alignment value that is not 0 or 1, then
the caller guarantees that both the source and destination pointers are aligned
to that boundary.

Semantics:

The 'llvm.memcpy.*' intrinsics copy a block of memory from the source
location to the destination location, which are not allowed to overlap. It
copies "len" bytes of memory over. If the argument is known to be aligned to
some boundary, this can be specified as the fourth argument, otherwise it should
be set to 0 or 1.

Syntax:

Overview:

The 'llvm.memmove.*' intrinsics move a block of memory from the source
location to the destination location. It is similar to the
'llvm.memcpy' intrinsic but allows the two memory locations to overlap.

Note that, unlike the standard libc function, the llvm.memmove.*
intrinsics do not return a value, and takes an extra alignment argument.

Arguments:

The first argument is a pointer to the destination, the second is a pointer to
the source. The third argument is an integer argument
specifying the number of bytes to copy, and the fourth argument is the alignment
of the source and destination locations.

If the call to this intrinisic has an alignment value that is not 0 or 1, then
the caller guarantees that the source and destination pointers are aligned to
that boundary.

Semantics:

The 'llvm.memmove.*' intrinsics copy a block of memory from the source
location to the destination location, which may overlap. It
copies "len" bytes of memory over. If the argument is known to be aligned to
some boundary, this can be specified as the fourth argument, otherwise it should
be set to 0 or 1.

Syntax:

Overview:

The 'llvm.memset.*' intrinsics fill a block of memory with a particular
byte value.

Note that, unlike the standard libc function, the llvm.memset intrinsic
does not return a value, and takes an extra alignment argument.

Arguments:

The first argument is a pointer to the destination to fill, the second is the
byte value to fill it with, the third argument is an integer
argument specifying the number of bytes to fill, and the fourth argument is the
known alignment of destination location.

If the call to this intrinisic has an alignment value that is not 0 or 1, then
the caller guarantees that the destination pointer is aligned to that boundary.

Semantics:

The 'llvm.memset.*' intrinsics fill "len" bytes of memory starting at
the
destination location. If the argument is known to be aligned to some boundary,
this can be specified as the fourth argument, otherwise it should be set to 0 or
1.

Overview:

The 'llvm.sqrt' intrinsics return the sqrt of the specified operand,
returning the same value as the libm 'sqrt' functions would. Unlike
sqrt in libm, however, llvm.sqrt has undefined behavior for
negative numbers (which allows for better optimization).

Arguments:

The argument and return value are floating point numbers of the same type.

Semantics:

This function returns the sqrt of the specified operand if it is a nonnegative
floating point number.

Overview:

The 'llvm.powi.*' intrinsics return the first operand raised to the
specified (positive or negative) power. The order of evaluation of
multiplications is not defined. When a vector of floating point type is
used, the second argument remains a scalar integer value.

Arguments:

The second argument is an integer power, and the first is a value to raise to
that power.

Semantics:

This function returns the first value raised to the second power with an
unspecified sequence of rounding operations.

Overview:

The 'llvm.bswap' family of intrinsics is used to byte swap integer
values with an even number of bytes (positive multiple of 16 bits). These are
useful for performing operations on data that is not in the target's native
byte order.

Semantics:

The llvm.bswap.i16 intrinsic returns an i16 value that has the high
and low byte of the input i16 swapped. Similarly, the llvm.bswap.i32
intrinsic returns an i32 value that has the four bytes of the input i32
swapped, so that if the input bytes are numbered 0, 1, 2, 3 then the returned
i32 will have its bytes in 3, 2, 1, 0 order. The llvm.bswap.i48,
llvm.bswap.i64 and other intrinsics extend this concept to
additional even-byte lengths (6 bytes, 8 bytes and more, respectively).

Overview:

The 'llvm.part.select' family of intrinsic functions selects a
range of bits from an integer value and returns them in the same bit width as
the original value.

Arguments:

The first argument, %val and the result may be integer types of
any bit width but they must have the same bit width. The second and third
arguments must be i32 type since they specify only a bit index.

Semantics:

The operation of the 'llvm.part.select' intrinsic has two modes
of operation: forwards and reverse. If %loBit is greater than
%hiBits then the intrinsic operates in reverse mode. Otherwise it
operates in forward mode.

In forward mode, this intrinsic is the equivalent of shifting %val
right by %loBit bits and then ANDing it with a mask with
only the %hiBit - %loBit bits set, as follows:

The %val is shifted right (LSHR) by the number of bits specified
by %loBits. This normalizes the value to the low order bits.

The %loBits value is subtracted from the %hiBits value
to determine the number of bits to retain.

A mask of the retained bits is created by shifting a -1 value.

The mask is ANDed with %val to produce the result.

In reverse mode, a similar computation is made except that the bits are
returned in the reverse order. So, for example, if X has the value
i16 0x0ACF (101011001111) and we apply
part.select(i16 X, 8, 3) to it, we get back the value
i16 0x0026 (000000100110).

Overview:

The 'llvm.part.set' family of intrinsic functions replaces a range
of bits in an integer value with another integer value. It returns the integer
with the replaced bits.

Arguments:

The first argument, %val and the result may be integer types of
any bit width but they must have the same bit width. %val is the value
whose bits will be replaced. The second argument, %repl may be an
integer of any bit width. The third and fourth arguments must be i32
type since they specify only a bit index.

Semantics:

The operation of the 'llvm.part.set' intrinsic has two modes
of operation: forwards and reverse. If %lo is greater than
%hi then the intrinsic operates in reverse mode. Otherwise it
operates in forward mode.

For both modes, the %repl value is prepared for use by either
truncating it down to the size of the replacement area or zero extending it
up to that size.

In forward mode, the bits between %lo and %hi (inclusive)
are replaced with corresponding bits from %repl. That is the 0th bit
in %repl replaces the %loth bit in %val and etc. up
to the %hith bit.

In reverse mode, a similar computation is made except that the bits are
reversed. That is, the 0th bit in %repl replaces the
%hi bit in %val and etc. down to the %loth bit.

This intrinsic makes it possible to excise one parameter, marked with
the nest attribute, from a function. The result is a callable
function pointer lacking the nest parameter - the caller does not need
to provide a value for it. Instead, the value to use is stored in
advance in a "trampoline", a block of memory usually allocated
on the stack, which also contains code to splice the nest value into the
argument list. This is used to implement the GCC nested function address
extension.

For example, if the function is
i32 f(i8* nest %c, i32 %x, i32 %y) then the resulting function
pointer has signature i32 (i32, i32)*. It can be created as follows:

Syntax:

Overview:

This fills the memory pointed to by tramp with code
and returns a function pointer suitable for executing it.

Arguments:

The llvm.init.trampoline intrinsic takes three arguments, all
pointers. The tramp argument must point to a sufficiently large
and sufficiently aligned block of memory; this memory is written to by the
intrinsic. Note that the size and the alignment are target-specific - LLVM
currently provides no portable way of determining them, so a front-end that
generates this intrinsic needs to have some target-specific knowledge.
The func argument must hold a function bitcast to an i8*.

Semantics:

The block of memory pointed to by tramp is filled with target
dependent code, turning it into a function. A pointer to this function is
returned, but needs to be bitcast to an
appropriate function pointer type
before being called. The new function's signature is the same as that of
func with any arguments marked with the nest attribute
removed. At most one such nest argument is allowed, and it must be
of pointer type. Calling the new function is equivalent to calling
func with the same argument list, but with nval used for the
missing nest argument. If, after calling
llvm.init.trampoline, the memory pointed to by tramp is
modified, then the effect of any later call to the returned function pointer is
undefined.

Syntax:

Overview:

The 'llvm.var.annotation' intrinsic

Arguments:

The first argument is a pointer to a value, the second is a pointer to a
global string, the third is a pointer to a global string which is the source
file name, and the last argument is the line number.

Semantics:

This intrinsic allows annotation of local variables with arbitrary strings.
This can be useful for special purpose optimizations that want to look for these
annotations. These have no other defined use, they are ignored by code
generation and optimization.

Overview:

The 'llvm.annotation' intrinsic.

Arguments:

The first argument is an integer value (result of some expression),
the second is a pointer to a global string, the third is a pointer to a global
string which is the source file name, and the last argument is the line number.
It returns the value of the first argument.

Semantics:

This intrinsic allows annotations to be put on arbitrary expressions
with arbitrary strings. This can be useful for special purpose optimizations
that want to look for these annotations. These have no other defined use, they
are ignored by code generation and optimization.